1. Field of the Invention
The present invention relates to a sulfide solid electrolyte material that has high Li ion conductivity.
2. Description of Related Art
In recent years, as information-related devices and communication devices such as personal computers, video cameras, and portable telephones are rapidly spreading, a development of batteries used as power supply thereof is regarded as important. Further, also in an automobile industry and so on, batteries for electric automobiles or hybrid automobiles, which have high output and high capacity, are under development. At the present time, among various kinds of batteries, lithium batteries are under attention from the viewpoint of high energy density.
Lithium batteries that are commercially available at the present time use an electrolytic solution containing inflammable organic solvent, and accordingly, a safety device that can prevent the temperature from increasing at the time of short-circuiting has to be provided and an improvement in structure and material for preventing the short-circuiting is necessary. On the other hand, all-solid-state lithium batteries in which a solid electrolyte layer is used in place of the electrolytic solution do not contain inflammable organic solvent therein, and accordingly a safety device can be simplified. The all-solid-state lithium batteries are thus considered to be superior in production costs and productivity. Further, as solid electrolyte materials usable for the solid electrolyte layer like this, sulfide solid electrolyte materials have been known.
The sulfide solid electrolyte materials have high Li ion conductivity and are advantageous in realizing higher output of the battery, and accordingly, various studies have been conducted thereon. For example, in Tomei et al., “Preparation of Amorphous Materials in the system LiI—Li2S—P2S5 by Mechanical Milling and Their Lithium Ion Conducting Properties”, Proceedings of The Symposium On Solid State Ionics, Vol. 23, p. 26-27 (2003) (non-Patent Document 1), LiI—Li2S—P2S5 system amorphous materials obtained by mechanical milling are disclosed. Further, in F. Stader et al., “Crystalline halide substituted Li-argyrodites as solid electrolyte for lithium ion batteries”, 216th ECS (The Electrochemical Society) Meeting with EuroCVD 17 and SOFC XI-11th International Symposium On Solid Oxide Fuel Cells, 2009, http://www.electrochem.org/meetings/scheduler/abstracts/216/0590.pdf (non-Patent Document 2), crystalline materials represented by Li6PS5X (X=Cl, Br, I) are disclosed.